The demands of semiconductor manufacture have required the use of high performance surfactants and wetting agents in photoresist developer formulations. As line features shrink to smaller sizes and photoresist substrate materials become more aliphatic in nature (i.e. having lower surface energy), aqueous developer solutions are being formulated with surface tension reducing agents. Another requirement for these developers is that they have a low tendency to foam. This is accentuated by the movement toward larger wafer sizes. Low foam formation is particularly important when using spray-puddle techniques because microbubble entrainment during spreading of the solution over the photoresist surface can lead to defects. Surfactants that have been used in the past to increase wetting of the photoresist typically lead to higher foam formation. For the most part the industry has focused on the effect of surfactant on photoresist performance, such as contrast, critical dimension, and feature sharpness. Although the cleaning ability of underlying substrates is enhanced by typical surfactants, foam formation still remains a problem.
Tetramethylammonium hydroxide (TMAH) is the chemical of choice in aqueous alkaline solutions for developing photoresists according to Microlithography, Science and Technology, edited by J. R. Sheats and B. W. Smith, Marcel Dekker, Inc., 1998, pp 551-553. Surfactants are added to the aqueous TMAH solutions to reduce development time and scumming and to improve surface wetting.
U.S. Pat. No. 5,985,968 discloses the use of 1,1-dialkyl ureas to reduce equilibrium and dynamic surface tension in aqueous compositions.
U.S. Pat. No. 5,972,431 discloses the use of certain cyclic ureas to reduce equilibrium and dynamic surface tension in aqueous compositions.
There are few references describing low foam surfactants in photoresist developer compositions. JP 10-319606 discloses that commercially available ethylene oxide (EO)/propylene oxide (PO) block polymers give good wetting and low foam.
JP 03-062034 discloses polyoxyalkylene dimethyl polysiloxanes as good surfactants with low foam in photoresist developer formulations. Polysiloxanes are known to rearrange or decompose under conditions of high pH.
Although there are a few references to the use of ureas in photoresist developer compositions, they are not related to the use as surface active agents.
U.S. Pat. No. 4,997,748 discloses cyclic nitrogen compounds at levels of 0.1 to 10 wt % to decrease scum formation and enhance image sharpness during photoresist development. Among the cyclic nitrogen compounds taught is the cyclic urea 1,3-dimethyl-2-imidazolidinone. Since the nitrogen compounds are not amphipathic, it is not likely that they will lower surface tensions at low concentrations, and their utility appears to be based on properties other than surface tension reduction. 1,3-dimethyl-2-imidazolidinone is well known as a very good solvent and not as a surface-active material.
Maekawa et al, "Dissolution Inhibitory Effect of Urea Additives on a Carboxyl Polymer Through a Supramolecular Structure", disclose the use of 1,3-disubstituted ureas to modify the dissolution characteristics of photosensitive carboxyl-polymers in TMAH solution. The amounts of the ureas were not specified, but it is clear that their role is to actively bind to the resin and not to lower the surface tension of the developer.